Troubleshoot when your thermostat won’t turn on

If your thermostat won’t turn on and you see a blinking red or green light, or no light at all, there could be a power issue or your thermostat may have frozen during a software update. Here’s how to troubleshoot.

If there’s a power issue, your thermostat’s battery will drain and it will turn off Wi-Fi, the display and other features to preserve battery life.

Before you start troubleshooting:

  • Your Nest thermostat should automatically turn on once it’s plugged into a live power socket (installed on a stand) or connected to live Heat Link wires (installed on the wall). You’ll need to connect the Heat Link to the app and set it up before it will control your heating system.
  • If you see a blinking red light at the top of your Nest thermostat’s display, you’ll need to wait until the battery is charged before you can use it to control heating.
  • You can manually turn on heating if needed. Just press the button on the Heat Link to turn on heating while you troubleshoot. Go to How to manually turn heating on or off for more information.
  • During regular use your thermostat’s screen may automatically turn off after a period of inactivity, but it should also automatically turn back on when it senses someone is nearby or when someone uses the app to control it.
  • Depending on the installation, your Nest thermostat either uses the USB power cable (when it’s on the Nest Stand), or wires from  the Heat Link (when installed on the wall), to keep its internal battery charged. If the power is switched off or there’s a blackout, the battery has enough capacity to keep working for a while. Your thermostat will also turn off features like Wi-Fi to preserve battery life before it must turn off completely.
  • If you see an error message on your thermostat or in the app, follow the troubleshooting steps in Troubleshooting Nest thermostat error codes.
  • Use the troubleshooting steps below only if your thermostat is unresponsive when you turn the ring or press the screen.

If there’s a blinking red light on your thermostat

A blinking red light at top of your thermostat’s display means that the battery charge is very low but it’s being charged.

Your thermostat should automatically turn on

As long as you see a blinking red light, there’s typically nothing wrong with your Nest thermostat installation, but the internal battery is low on charge. Your thermostat should automatically turn on when the battery is charged enough.

If the blinking red light persists or keeps coming back

The troubleshooting steps are different depending on how your thermostat is installed and powered.
Plugged into a power socket - installed on a stand
  1. Check that the power socket your thermostat is plugged into isn’t being switched off and on. This can cause the battery to drain while it’s off, and require charging when switched back on.
  2. Try plugging your thermostat into a different power socket. If that fixes the issue, there may be an issue with the original socket that needs to be addressed by an electrician.
  3. Contact a local Nest Pro, who can properly diagnose your heating system and your Nest thermostat.

Powered by Heat Link wires - installed on the wall​

  1. Check that the Heat Link is receiving power. Press the button on your Heat Link. If the light turns on, it’s receiving power. If not, make sure the fuse that controls power to your system is set to on.
  2. Pull off the Nest display and use the USB port on the back to charge it with a USB cable and wall charger. Depending on the model you have it will be either mini or micro USB.
    Note: Do not use a computer USB port or other unpowered USB port for charging.
  3. The the display should eventually light up with a message asking you to connect it to the base. 
  4. Reconnect the display to the thermostat base. Make sure you press firmly until you hear it click into place and check that it’s fully seated.
  5. If the blinking red light returns again, turn off power to your system and Heat Link. Pull off the thermostat display and check that the wires connected to the thermostat base are fully seated and that the screws holding them are snug.
  6. If the issue persists, contact our support team for further help.

If there’s a blinking green light on your thermostat

Your thermostat should automatically turn on

A blinking green light at the top of your Nest thermostat’s display means that it’s updating the software, starting up or restarting. Typically, this will only last a minute or two. Once your thermostat has finished starting
up, the display will turn on.

If the light is blinking green and your thermostat is unresponsive for more than five minutes, it may have frozen during the update.

  1.  Try removing and reconnecting the display. Pull it straight off the base. Make sure the pin connector is lined up correctly and push it back onto the base. You should hear a click to confirm it’s properly seated.
  2. If reconnecting the display doesn't help, press down on the thermostat display for 10 seconds then release it. This will force your thermostat to restart. For more details, please see the following article:

How to restart or reset Nest thermostats

If there’s no light on your thermostat

If there’s no blinking light on your thermostat, and it’s unresponsive and won’t turn on, the battery has drained and that there’s no power being delivered to it.

1. Check that the display is properly connected to the base

If the display isn’t fully seated on the base, your thermostat won’t turn on and can’t charge its battery.

  1. Remove the display (pull it straight off).
  2. Make sure the pin connector is lined up correctly and push it straight back onto the base. You should hear a click to confirm it’s properly seated.

2. Check that the thermostat is receiving power

Troubleshooting steps are different depending on how your thermostat is installed and powered.
Plugged into a power socket - installed on a stand
  • Make sure the thermostat’s USB power cable is pushed all the way into the Nest thermostat. Also check that the other end of the cable is fully inserted into the power adapter.
  • Make sure the plug is fully plugged into a power socket that is on. Some power sockets can be switched on and off. Check that the socket is switched on. 
    Note: We recommend that you plug your Nest thermostat into an unswitched outlet when possible.
  • There may be a wiring issue with the socket. Use a lamp or other electronic device to make sure that the socket is live. If not, check that the fuse controlling power to the socket isn’t blown. Replace it if needed.
Powered by Heat Link wires- installed on the wall
  1. Check that the Heat Link is receiving power. Press the button on your Heat Link. If the light comes on, it’s receiving power. If not, Make sure the fuse that controls power to your Heat Link is set to on.
  2. Pull off the Nest display and use the USB port on the back to charge it with a USB cable and wall charger. Depending on the model you have it will be either mini or micro USB.
  3. Note: Do not use a computer USB port or other unpowered USB port for charging.
  4. The the display should eventually light up with a message asking you to connect it to the base. 
  5. Reconnect the display to the thermostat base. Make sure you press firmly until you hear it click into place.
  6. If your thermostat remains unresponsive, turn off power to your system and Heat Link. Pull off the thermostat display and check that the wires connected to the thermostat base are fully seated and secured.
  7. If the issue persists, contact a local Nest Pro to check your installation.

 3. Check if your Nest thermostat is damaged

In rare cases, a Nest thermostat can be damaged.

  1. Check for damage on the plug and USB cable. You can try a different USB power adapter if the plug is damaged. Use one that’s rated to deliver 1.4 Amps at 5 V. If you have a Nest Learning Thermostat, you can also swap out the USB cable if it’s damaged.
  2. If your Nest thermostat appears damaged, and it’s still under warranty, you may be eligible for a replacement. Contact us to see if you qualify.

Contact a Nest Pro for help

If these steps don’t resolve the problem, you should contact a local Nest Pro. The problem may be caused by a problem with your system.
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